U.S. patent application number 12/112285 was filed with the patent office on 2009-11-05 for distributed load balancing in wireless networks.
This patent application is currently assigned to ARUBA NETWORKS, INC.. Invention is credited to Subburajan Ponnuswamy.
Application Number | 20090274129 12/112285 |
Document ID | / |
Family ID | 41257032 |
Filed Date | 2009-11-05 |
United States Patent
Application |
20090274129 |
Kind Code |
A1 |
Ponnuswamy; Subburajan |
November 5, 2009 |
DISTRIBUTED LOAD BALANCING IN WIRELESS NETWORKS
Abstract
Distributed load balancing in wireless digital networks. In a
network having a plurality of access nodes with at least one
wireless client connected to a first access node, the client is
encouraged to move to a different access node by reducing the
apparent signal strength of transmissions from the access node to
the client. Apparent signal strength can be reduced by reducing
transmit power, by using beam forming, antenna switching, or a
combination. Other access nodes may send unsolicited frames, such
as probe response frames to the client, encouraging the client to
move.
Inventors: |
Ponnuswamy; Subburajan;
(Scotts Valley, CA) |
Correspondence
Address: |
BLAKELY SOKOLOFF TAYLOR & ZAFMAN LLP
1279 OAKMEAD PARKWAY
SUNNYVALE
CA
94085-4040
US
|
Assignee: |
ARUBA NETWORKS, INC.
Sunnyvale
CA
|
Family ID: |
41257032 |
Appl. No.: |
12/112285 |
Filed: |
April 30, 2008 |
Current U.S.
Class: |
370/338 |
Current CPC
Class: |
Y02D 70/146 20180101;
Y02D 30/70 20200801; Y02D 70/142 20180101; H04W 16/08 20130101;
H04W 36/22 20130101 |
Class at
Publication: |
370/338 |
International
Class: |
H04Q 7/24 20060101
H04Q007/24 |
Claims
1. In a wireless digital network having a plurality of access nodes
and at least one wireless client connected to a first access node
in the plurality of access nodes, a method of encouraging the
wireless client to connect to a different access node comprising
reducing the signal strength of at least those transmissions from
the first access node to the wireless client.
2. The method of claim 1 where the step of reducing the signal
strength of at least those transmissions from the first access node
to the wireless client further comprises reducing transmit power at
the first access node for at least those transmissions to the
wireless client.
3. The method of claim 1 where the step of reducing the signal
strength of at least those transmissions from the first access node
to the wireless client further comprises reducing transmit power at
the first access node for only those transmissions to the wireless
client.
4. The method of claim 1 where the step of reducing the signal
strength of at least those transmissions from the first access node
to the wireless client further uses antenna switching or
beamforming.
5. The method of claim 1 where the step of reducing the signal
strength of at least those transmissions from the first access node
to the wireless client further comprises reducing the transmit
power on beacon frames transmitted by the first access node.
6. The method of claim 1 further including the step of causing at
least one of the remaining access nodes to transmit unsolicited
frames to the wireless client.
7. The method of claim 6 where the unsolicited frames are probe
response frames.
8. The method of claim 6 where the at least one of the remaining
access nodes transmits unsolicited frames to the wireless client
using beamforming or antenna switching.
9. The method of claim 6 where the step of causing at least one of
the remaining access nodes to transmit unsolicited frames to the
wireless client is mediated by the first access node.
10. The method of claim 6 where the step of causing at least one of
the remaining access nodes to transmit unsolicited frames to the
wireless client is mediated by a central controller connected to
each of the plurality of access nodes.
11. A machine readable medium having a set of instructions stored
therein, which when executed on a system having a plurality of
access nodes and at least one wireless client connected to a first
access node, causes a set of operations to be performed comprising
instructing the first access node to reduce signal strength for at
least those transmissions to the wireless client.
12. The machine readable medium of claim 11 wherein the set of
instructions causes a set of operations further comprising
instructing the first access node to reduce signal strength for at
least those transmissions to the wireless client by reducing
transmit power.
13. The machine readable medium of claim 11 wherein the set of
instructions causes a set of operations further comprising
instructing the first access node to reduce signal strength for at
least those transmissions to the wireless client by using
beamforming or antenna switching.
14. The machine readable medium of claim 11 wherein the set of
instructions causes a set of operations further comprising
instructing the first access node to reduce signal strength for
only those transmissions to the wireless client by reducing
transmit power.
15. The machine readable medium of claim 11 wherein the set of
instructions causes a set of operations further comprising
instructing one of the remaining access nodes to transmit
unsolicited frames to the wireless client.
16. The machine readable medium of claim 15 where the unsolicited
frames are probe response frames.
17. The machine readable medium of claim 15 where the at least one
of the remaining access nodes transmits unsolicited frames using
beamforming or antenna switching.
18. The machine readable medium of claim 15 where the step of
causing at least one of the remaining access nodes to transmit
unsolicited frames to the wireless client is mediated by the first
access node.
19. The machine readable medium of claim 15 where the step of
causing at least one of the remaining access nodes to transmit
unsolicited frames to the wireless client is mediated by a central
controller connected to each of the plurality of access nodes.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to the operation of wireless
digital networks, and more particularly to load balancing in
wireless digital networks.
[0002] A wireless digital network typically comprises a plurality
of wireless access nodes providing services to wireless clients.
Access nodes may have wired or wireless connections to the
services, and may connect to a central controller, or the control
function may be distributed among the access nodes. Wireless client
devices obtain service by connecting through an access node.
[0003] In today's wireless networks, the decision to move a client
from one access node to another access node is taken entirely by
the client. If an access node wishes to move a currently connected
client to another access node, for example to provide better
service, to balance loading, or for other reasons, the access node
currently connected to the client must actively disconnect or
de-authenticate the client, forcing the client to re-connect.
[0004] Such active disconnection or de-authentication can result in
session timeouts, increased communications latency, increased
roaming latency, and dissatisfied users.
[0005] What is needed is a method of load balancing in wireless
networks that does not rely on active disconnects.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The invention may be best understood by referring to the
following description and accompanying drawings that are used to
illustrate embodiments of the invention in which:
[0007] FIG. 1 shows a block diagram of an electronic system.
DETAILED DESCRIPTION
[0008] Embodiments of the invention relate methods of load
balancing in wireless digital networks. In one embodiment, clients
are encouraged to move away from their currently connected access
node by altering signal strengths. The access node currently
supporting the client may reduce transmit power on transmissions to
that client. This may be accomplished by reducing transmit power,
switching antennas, beam forming, or a combination of these
techniques. Other access nodes may increase transmit power, use
beam forming, or send unsolicited probe response or other frames to
the client, advertising availability.
[0009] According to the present invention and as shown in FIG. 1
and the descriptions following, access nodes 100, 102, 104 support
wireless clients such as wireless client 300. As is known to the
art, access node 100 is a digital device with a central processing
unit (CPU) 110, memory hierarchy 120, network interface 130, and
wireless interface 140. In one embodiment, CPU 110 is a MPS-class
CPU, which may be supplied from companies such as Cavium or Raza
Microelectronics. Other CPUs may also be used, such as those from
Intel AMD, IBM, and the like. Memory hierarchy 120 contains data
and instructions to operate access node 100, and contains both
volatile and non-volatile memory elements. As known to the art,
high-speed volatile memory such as RAM or DRAM is used to store
data and instructions temporarily, while non-volatile memory such
as flash, ROM, and/or EPROM is used to store longer duration
information such as that required to start up the device, and files
for continued operation. Network interface 130 is used to
communicate with central services and other access nodes, and is
typically a wired Ethernet interface, or a wireless interface such
as an IEEE 802.11 wireless interface, a WiMAX or EVDO interface, or
the like. Wireless interface 140 is typically an IEEE802.11
wireless interface. Access nodes 100, 102, 104 typically operate
under control of an operating system such as a Linux operating
system, or other operating system suitable for use in embedded
devices, such as VxWorks provided by Wind River systems.
[0010] In one embodiment of the invention, access nodes 100, 102,
104 operate cooperatively, communicating through switch 200. In
such an embodiment, switch 200, which may be a switch, router, hub,
or other network data switching device, does not provide
centralized control, but merely assists in the passage of data
among devices. In another embodiment of the invention, access nodes
100, 102, 104 connect to a network controller 200, which is a
digital system of similar internal architecture to access nodes
100, 102, 104, but usually with increased capability, and provides
centralized management and control of a plurality of wireless
access nodes 100, 102, 104.
[0011] Wireless client device 300 is similarly a digital system
comprising CPU 310, memory hierarchy 320, wireless interface 330,
and peripherals 340. Wireless client 300 may be a device such as an
Wi-Fi phone, a hand-held wireless scanner, a hand-held or laptop
computer, or other wireless device. In such a wireless device, the
choice of CPU 310 will depend on the chosen function. CPUs from
Intel and AMD are popular for laptop computers, for example. Memory
hierarchy 320, while containing a mix of non-volatile and volatile
memory elements, will also be formed for the desired function, with
hard disk drives and large non-volatile solid state memories used
in laptops, while other devices may use compact flash and other
non-volatile devices in addition to high-speed volatile memories
such as DRAM. Wireless interface 330 is typically an IEEE 802.11
Wi-Fi interface for communicating with access nodes 100, 102, 104
and similar wireless devices. Peripherals 340 may include
keyboards, displays, purpose built scanners for devices such as
hand-held wireless scanners, pointing devices, and the like.
[0012] In operation, client 300 accesses information wirelessly
through interfaces 330, 140, in this example according to
IEEE802.11 standards. Client 300 establishes a connection with an
access node, in this example with access node 100, which provides
access to required data and services. As known in the art in
current wireless networks, the decision to move from one access
node to another, say from access node 100 to access node 102, is
taken entirely by client 300.
[0013] If access node 100 wishes to move client 300 to another
access node, it must actively disconnect or de-authenticate client
300, forcing client 300 to reconnect somewhere else. Those familiar
with the art will understand that such disconnection and/or
de-authentication will usually happen at the worst possible time
according to client 300 and its user, resulting in session
timeouts, lost data, broken connections, increased latency, and
unhappy users.
[0014] The decision to move a client from one access node to
another may be made for a myriad of reasons, among them load
balancing, providing better response, and the like. As examples,
access nodes may be configured to handle a maximum pre-determined
number of clients per access node, or a pre-determined ratio of
clients over a set of access nodes. Clients may be moved among
access nodes to group those clients based on actual or projected
load, or PHY type, or other capabilities. Clients may be moved
among access nodes based on traffic type; as an example, it may be
beneficial to group voice clients together on one or more access
nodes, and on non-DFS channels. The reasoning behind the decision
to move a client away from a particular access node is not
important to understanding the present invention.
[0015] According to the present invention, a client connected to an
access node is encouraged to move to another access node by
altering signal strengths so that the client will move to another
access node. This takes advantage of the client's use of signal
strength as an important criteria used to choose among access
nodes, as observed in beacon or other frames.
[0016] In one embodiment of the invention, transmit power on frames
sent to at least a particular client is lowered. In the example of
FIG. 1, access node 100 would lower transmit power through wireless
interface 140 on at least the frames sent to client 300. Lower
transmit power means lower received signal strength. While it is
preferable that only the frames sent to the particular client, such
as client 300, be sent at a lower power level, some access nodes
may not allow this fine a granularity of transmit power control. It
may be useful or necessary to reduce transmit power in a series of
steps.
[0017] In another embodiment of the invention, with access nodes
supporting beamforming, or having switchable antennas such as
sectorized antennas, the signal strength seen by the client may be
reduced by switching antennas or antenna patterns in at least the
frames transmitted to that client such that the client sees signals
with lower signal strength. Beamforming and/or antenna switching
techniques may also be used by other access nodes to present
stronger signals to the targeted client.
[0018] In another embodiment of the invention, one or more access
nodes operating on the same channel may be commanded to send
unsolicited probe responses or similar frames which indicate
availability and/or capability to the client, in essence
advertising their availability. In one embodiment, such
coordination among access nodes may be coordinated by the access
node currently supporting the wireless client. In another
embodiment where the access nodes are connected and operated by a
central controller, such coordination is mediated by the central
controller.
[0019] While the invention has been described in terms of various
embodiments, the invention should not be limited to only those
embodiments described, but can be practiced with modification and
alteration within the spirit and scope of the appended claims. The
description is this to be regarded as illustrative rather than
limiting.
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